BANGOR, Maine — Using a computer demonstration, a forensic analyst from the Maine State Police Crime Lab in Augusta explained to jurors Monday afternoon how she matched a small piece of plastic found at the site of a fatal Orono hit-and-run, the other on the victim’s clothes — to a York County man’s truck.

Cynthia Homer testified on the fourth day of the trial of Garrett Cheney, 23, of South Berwick at the Penobscot Judicial Center. She told the jury that the break pattern on the end of the piece of gray waffle-shaped plastic found on the victim’s clothing fit perfectly into a broken section of the grille recovered from Cheney’s 2003 Chevrolet Silverado pickup truck. The piece was found when the victim was undressed and her clothing placed into evidence bags at the State Medical Examiner’s Office, Orono police Detective Andrew Whitehouse testified last week.

Cheney is charged with manslaughter, aggravated criminal operating under the influence of intoxicants, leaving the scene of an accident that resulted in serious bodily injury, and criminal operating under the influence of intoxicants in connection with the death of Jordyn Bakley, 20, of Camden.

The forensic analyst also used a series of photographs to demonstrate how a small piece of black plastic matched a different part from Cheney’s truck — the passenger’s side headlight bracket. That evidence was collected from a snowbank at the scene.

During her testimony Monday, Homer talked the jury through a series of photographs projected onto one large movie-type screen on a wall in the courtroom and several small flat-screen monitors placed in the jury box. The forensic analyst explained how she carefully examined the evidence to conclude it matched parts removed from Cheney’s truck.

Bakley’s body was found about 5:30 a.m. Jan. 30, 2010, in front of 15 Middle St. by a newspaper carrier, according to previous testimony. Investigators have theorized that she was struck and killed between about 3 and 3:20 a.m. based on the outgoing and incoming calls on her cellphone, which was found open about 20 feet from her body.

Cheney’s truck went off the road about 3:30 a.m. that same day on southbound Interstate 95 in Etna.

A Brewer truck driver testified Monday that he called 911 about 3:20 a.m. Jan. 30, 2010, to report an erratic driver in front of him on the highway.

“The driver was going between 40 and 50 miles per hour, going from one lane to another,” Donald Webster, who was driving mail from Hampden to Waterville, told the jury. “It was the most erratic driving I’ve ever seen in my life.”

In addition to Webster, Ronald Sawyer of Hampden told the jury that about 3:30 a.m. Jan. 30, 2010, he stopped between mile markers 165 and 166 on I-95 south when he saw what turned out to be Cheney’s pickup truck off the road in the median.

Sawyer, who dropped Cheney off at the Irving station in Newport, said he was on his way to a snowmobile race in New Hampshire when he saw the pickup off the highway.

Cheney, who was uninjured, called 911 using his own cell phone while he sat in Sawyer’s truck. His speech on the 911 call, played for the jury Monday, was slurred.

Sawyer described Cheney as “dazed.”

Maine State Trooper Forrest Simpson testified that he charged Cheney with drunken driving because he smelled alcohol on the defendant, Cheney’s speech was slurred, his eyes were red and glassy, and he had driven his car off the road.

In addition, Simpson told jurors that when he asked Cheney to rate his own sobriety on a scale of one to 10 — with one being “stone cold sober” and a 10 being “totally hammered” — Cheney rated his own sobriety a five. The trooper said that when he administered a breath test at the Newport Police Department between 5 and 5:15 a.m., Cheney’s blood alcohol content measured 0.15 percent, nearly twice the legal limit of 0.08 percent.

In his opening statement at the trial, defense attorney William T. Bly of Biddeford conceded that Cheney was operating under the influence of intoxicants when he ran his truck off the road.

Cheney was in Orono on Jan. 29 into the early morning hours of Jan. 30 visiting his cousin Nathan Messier, 22, of South Berwick to celebrate Messier’s 21st birthday, Messier told the jury Monday.

Messier said that he, Cheney and Colin Kelsey, 22, of Orono went to the Bear Brew Pub and Woodman’s, both restaurants with bars in downtown Orono, after stopping at Kelsey’s apartment at 38 Middle St. Messier told the jury that he and Cheney had a “double shot of Jagermeister” before walking the short distance to the pub on Main Street.

Kelsey said that when he got home at 1:30 a.m. Jan. 30, 2010, from drinking at the bars and later, at a party, he was “intoxicated.”

Bakley lived at 27 Middle St. in Orono. Her body was found in front of 15 Middle St.

The state is expected to rest Tuesday, Penobscot County District Attorney R. Christopher Almy said Monday after the trial recessed for the day.

Bly said he expected it would take two days or so for the defense to present its case to the jury.

The jury could begin deliberating Thursday or Friday.

If convicted, Cheney faces up to 30 years in prison on the manslaughter charge alone.

Click here to watch a slide show of how Cynthia Homer matched small pieces of plastic — one found at the site of a fatal Orono hit-and-run, the other on the victim’s clothes — to Garrett Cheney’s 2003 Chevrolet Silverado pickup truck.